1. Field of the Invention
The present invention generally relates to image signal processing and image signal circuits, and, more particularly, to tuning signal processing and tuning circuits with small output drive currents exhibiting increased drive current capacitance at an output terminal.
2. Description of the Related Art
Typically, a tuning circuit in a video tape recorder (i.e., a VCR) includes an radio frequency converter, a tuner and a demodulator. A broadcasting signal received by an antenna is output to a radio frequency amplifier and an output mode switch through a distributor. The RF converter includes the distributor, an output switch, and a modulator. The tuner includes the RF amplifier, a mixer, and a local oscillator while the demodulator includes a surface acoustic wave (i.e., a SAW) filter, a demodulator, an output buffer, and frequently, an external buffer that is often necessary to provide a current necessary to drive some external appliances that is larger than can be obtained with the output buffer included in the integrated circuit.
In the operation of a typical tuning circuit constructed as an integrated cirucit, a broadcast signal is amplified at its radio frequency, mixed with a local oscillation frequency signal of a channel predetermined by the local oscillator in order to convert the broadcast signal into an intermediate frequency. The intermediate frequency is then demodulated. The demodulated video signal is applied through the internal output buffer that provides a small drive current of between approximately 0.5˜1 milli-Amperes. A selection switch selects a video signal to apply to a video signal processor from between the video signal from the tuner circuit or a video input signal applied to an input video jack. When the tuner circuit is constructed as an integrated circuit, an externally connected circuit can be driven with a driving current of approximately 0.5˜1 milli-Amperes; this range of amplitudes is common in integrated circuits. I have noticed that if a circuit connected to the integrated tuner circuit should happen to require a driving current of 10 milli-Amperes or more however, an external buffer must be incorporated into the tuner circuit between the output buffer in order to obtain a sufficiently large driving current from the integrated circuit. I have found that absent the external buffer, the ability of the integrated tuning circuit deteriorates to the point that attenuation occurs in the high frequency signal components of the video signal, thereby markedly reduces the gain of the higher frequency characteristics of the video signal.